Among the various kinds of semiconductor devices, one type that is well known in the art is the insulated gate, field effect transistor. For example, this type of transistor and its operation are described by S. R. Hofstein and F. P. Heiman in an article entitled "The Silicon Insulated-Gate Field-Effect Transistor" appearing in the Proceeding of the IEEE, 51, p. 1190 (September 1963). Furthermore a number of patents, such as U.S. Pat. Nos. 3,411,199; 3,472,712 and 3,513,364, have issued that describe methods for fabricating such semiconductor devices. This type of transistor is generally characterized by an arrangement in which the source and drain are spaced apart regions of the same conductivity formed on the same surface of a semiconductor body. The gate is positioned over the space between the source and drain regions and is separated therefrom by a layer of insulating material. The layer of insulating material is usually in the form of an oxide of the same element as the semiconductor body. For example, when the semiconductor body is silicon, the insulator for the gate is silicon dioxide. In preparing the silicon dioxide insulating layer, the usual practice is to oxidize the exposed surface of the silicon body. In order to fabricate a field effect transistor having reliable and reproducible characteristics, it is important that the insulator be of high purity. The introduction of trace contaminants, such as alkali ions, into the silicon dioxide, which may occur during the oxidation procedure, causes the silicon dioxide to be unstable. Because of the ion drift and surface instabilities in the silicon dioxide insulator, the field effect transistors made by prior art procedures are not always completely reliable.
It is an object of this invention to provide an improved method for the fabrication of an insulated gate, field effect device.
Another object of the invention is to provide an insulated gate, field effect transistor of improved reliability.